Calculator
Tiny house loft and floor area check
Enter the inside dimensions of your plan to see how it lines up with the tiny house rules in an optional appendix of the International Residential Code. The result updates as you type, and nothing leaves your device.
160 sq ft floor area
Worked example (shown when scripts are off): a 20 ft by 8 ft house is 160 square feet, well under 400. A loft 8 ft long and 8 ft wide with a 1.5 ft sloped edge counts as 8 by 6.5, which is 52 square feet, above the 35 square foot minimum.
Before you decide
This is a planning check, not a code review. Many towns have not adopted this appendix, and a house on wheels is usually treated under different rules. Your local building department decides what applies to you.
The rules, in plain words
The checks follow the tiny house appendix (Appendix Q) of the 2018 and later International Residential Code. It defines a tiny house as a dwelling of 400 square feet or less of floor area, not counting lofts. Living areas and hallways need a ceiling at least 6 feet 8 inches high. A sleeping loft needs at least 35 square feet of floor, and portions of a sloped loft ceiling lower than 3 feet from the finished floor do not count toward that area. As we read it, a loft also needs at least 5 feet in any horizontal direction. The calculator uses all of these.
How the numbers are worked out
- Floor area is length times width. It is compared with 400 square feet.
- The ceiling height is compared with 6 ft 8 in, which is 6.67 ft.
- Usable loft width is the loft width minus the sloped edge that is under 3 ft high. Usable loft area is loft length times usable width, compared with 35 square feet.
- The smaller of the loft length and the usable width is compared with 5 feet.
For example, an 8 ft by 8 ft loft with a 3 ft sloped edge has 8 by 5, or 40 square feet, and passes. The same loft with a 4 ft sloped edge has 8 by 4, or 32 square feet, and falls 3 square feet short.
What it does not check
The appendix has more requirements than the three in this tool, including how you reach the loft (stairs, ladders or alternating tread devices), guards on open loft sides, and an emergency way out of sleeping lofts. The ceiling rule has other minimums for kitchens and bathrooms. Read the appendix text, or ask your building department, before you finalize a plan. See our guides on tiny house layouts and multi-use spaces for the daily-use side of the same numbers.
Why a pass is not enough
A loft that is 3 feet high at the edge meets the counting rule, but it is a place to lie down, not to sit up. Think about how you will get in and out, how warm air collects at the top, and whether you can live with a ceiling close to your face. Passing the minimum tells you the plan is not obviously out of bounds. It does not tell you the loft will be comfortable.
Where this comes from
We checked published summaries of Appendix Q of the 2018 International Residential Code, including a state building code council document and tiny house industry association pages, for the 400 square foot definition, the 6 ft 8 in ceiling, the 35 square foot loft minimum and the 3 foot sloped-ceiling rule. The 5 foot loft dimension is our reading of the appendix and should be confirmed in the code text. This is general information, not legal or building advice, and codes vary by place and edition.